Rivaroxaban, an inhibitor of coagulation factor Xa, promotes antitumor immunity in mice.

Antiphospholipid antibody syndrome is caused by antiphospholipid antibodies (aPLs) that cause thrombosis and pregnancy loss. In a Plenary Paper, Müller-Calleja et al dissect the complex and multifaceted mechanism by which aPLs induce thrombosis through priming of monocytes and disruption of the balance of tissue factor activation and inhibition.

Immune checkpoint inhibitors (ICI) significantly improved the prognosis of advanced melanoma patients. However, many patients do not derive long-term benefit from ICI therapy due to primary and acquired resistance. In this regard, it has been shown that coagulation factors contribute to cancer immune evasion and might therefore promote resistance to ICI. In particular, recent observations in murine systems demonstrated that myeloid-derived factor Xa (FXa) impedes anti-tumor immunity in the tumor microenvironment and that the oral FXa inhibitor (FXa-i) rivaroxaban synergizes with ICI. The synergistic effect of FXa inhibitors with clinical ICI therapy is unknown. We performed a retrospective study of 280 metastatic melanoma patients who were treated with ICI and stratified them for concomitant anticoagulation (AC) by medical chart review. Data on baseline patient characteristics, specific AC treatment, ICI therapy, other tumor-targeting therapies, and clinical outcomes were analyzed. Of 280 patients who received ICI, 76 received concomitant AC during initial ICI therapy. Patients on AC were treated either with heparins (n = 29), vitamin K antagonists (VKA) (n = 20), or FXa-i (n = 27). Patients requiring AC during ICI therapy showed no significantly reduced objective response rate (ORR) (p = 0.27), or progression-free (PFS; median PFS 4 vs. 4 months; p = 0.71) or overall survival (OS; median OS: 39 vs. 51 months; p = 0.31). Furthermore, patients who underwent AC did not show significantly more bleeding complications (p = 0.605) than those who were not anticoagulated. Remarkably, stratification of patients by the class of AC revealed that patients receiving FXa-i were more likely to obtain CR (26.9 vs. 12.6%, p = 0.037), and showed better ORR (69.2 vs. 36.4%, p = 0.005), PFS (median PFS: 12 months vs. 3 months; p = 0.006), and OS (median OS not reached vs. 42 months; p = 0.09) compared to patients not receiving FXa-i. Patient demographics and tumor characteristics in this patient subcohort did not significantly differ from patients not on FXa-i. In summary, our study provides first clinical evidence that the clinical application of FXa-i may enhance the efficacy of ICI therapy via the restoration of anti-tumor immunity, while patients who received FXa-i were not more likely to encounter bleeding complications.

Malignancies increase the risk for thrombosis and metastasis dependent on complex interactions of innate immune cells, platelets, and the coagulation system. Immunosuppressive functions of platelets and macrophage-derived coagulation factors in the tumor microenvironment (TME) drive tumor growth. Here we show that patients with malignancies and tumor-bearing mice have increased levels of coagulation factor (F) X expressing circulating monocytes engaged in platelet aggregate formation. This interaction and resulting thrombin generation on platelets interferes with monocyte differentiation and antigen uptake of antigen-presenting cells (APCs). Myeloid cell-specific deletion of FX or abrogated FXa signaling via protease activated receptor 2 (PAR2) averts the suppressive activity of platelets on tumor cell debris uptake and promotes the immune stimulatory activity of APCs in the TME. Myeloid cell FXa-PAR2 signaling deficiency specifically enhances activation of the cGAS-STING-IFN-I pathway with a resulting expansion of antigen experienced progenitor exhausted CD8⁺ T cells. Pharmacological blockade of FXa with direct oral anticoagulants expands T cell priming-competent immune cells in the TME and synergizes with the reactivation of exhausted CD8+ T cells by immune checkpoint inhibitors for improved anti-tumor responses. These data provide mechanistic insights into the emerging clinical evidence demonstrating the translational potential of FXa inhibition to synergize with immunotherapy.

Background All mature blood cells are derived from multipotent hematopoietic stem cells (HSCs) which are activated to meet the demand of the host during inflammation and injury. The endothelial cell protein C receptor (EPCR) is a marker for primitivity and quiescence of HSCs but the relative contributions of EPCR signaling versus anticoagulant functions in HSC maintenance are incompletely defined. Aims We aimed to dissect functions of EPCR by studying anticoagulant and signaling function in HSC of EPCR C/S mice carrying a single intracellular point mutation abolishing normal trafficking of EPCR through endo-lysosomal compartments. We assessed the contributions of EPCR signaling to stem cell maintenance by analyzing HSC mobilization and leukemia progression. Methods We studied the frequency and cell cycle activity of bone marrow (BM) hematopoietic stem and progenitor cells (HSPC) by multicolor flow cytometry. Furthermore, we analyzed changes in hematopoiesis in steady state, after granulocyte colony stimulating factor (G-CSF)-induced mobilization, in the context of aging and in the context of leukemia, using the MLL-AF9-induced acute myeloid leukemia (AML) model. Results HSCs, lungs and isolated lung-derived smooth muscle cells of EPCR C/S mice showed protein expression levels and anticoagulant function indistinguishable from wildtype (WT). We found an increase of circulating HSCs in the peripheral blood of EPCR C/S mice compared to control under steady state conditions. Isolated HSC displayed diminished polarization of CDC42 and VLA-4 (α 4β 1 integrin) affinity to VCAM-1 in EPCR C/S versus strain-matched EPCR wt mice, indicating that EPCR signaling directly controls HSC retention via integrin affinity to the BM niche. In addition, we noticed a higher cell cycle activity in myeloid-restricted progenitors of EPCR C/S mice compared to control. G-CSF treatment led to increased mobilization of both BM neutrophils and HSCs into the peripheral blood of EPCR C/S mice compared to EPCR wt mice. A myeloid bias was also seen in serially transplanted aged mice, resulting in increased frequencies of myeloid-biased progenitors in the BM of EPCR C/S mice compared to control mice, accompanied by an increase of circulating neutrophils in the blood. Consistent with higher cell cycle activity of myeloid progenitors and an overall increase of myeloid-biased output in EPCR C/S mice, induction of AML by retroviral transduction of EPCR C/S BM cells with MLL-AF9-expressing retrovirus resulted in an increase of cell cycle activity of Lin - MLL-AF9 + leukemic BM blasts and a higher leukemic load in the peripheral blood of mice transplanted with MLL-AF9 + EPCR C/S BM compared to control. As a result, MLL-AF9 + EPCR C/S leukemia showed a more aggressive disease with shortened survival times compared to control. In contrast, chemotherapy of MLL-AF9 + EPCR C/S leukemia reduced leukemic load in the peripheral blood and decelerated disease progression. These data demonstrate that increased leukemia cell cycle activity conferred chemosensitivity. Conclusion With a site-specific EPCR mutant knock-in mouse, we here demonstrate that EPCR signaling and anticoagulant function can be separated. We provide direct evidence that EPCR signaling plays a crucial role in maintaining HSC retention via VLA-4 affinity to VCAM-1, controls cell cycle activity and myeloid output in normal, stress-induced, and malignant hematopoiesis with implications for therapeutic approaches in acute myeloid leukemia. Disclosures: Ruf: MeruVasimmune: Other: Ownership Interest; ARCA bioscience: Consultancy, Patents & Royalties; ICONIC Therapeutics: Consultancy.